Fabricating method for a liquid crystal display of horizontal electric field applying type

ABSTRACT

A liquid crystal display having an applied horizontal electric field comprising: a gate line; a common line substantially parallel to the gate line; a data line arranged to cross the gate line and the common line to define a pixel area; a thin film transistor formed at each crossing of the gate line and the data line; a common electrode formed in the pixel area and connected to the common line; a pixel electrode connected to the thin film transistor, wherein the horizontal electric field is formed between the pixel electrode and the common electrode in the pixel area; a gate pad formed with at least one conductive layer included in the gate line; a data pad formed with at least one conductive layer included in the data line; a common pad formed with at least one conductive layer included in the common line; a passivation film to expose at least one of the gate pad, the data pad and the common pad; and a driving integrated circuit mounted on a substrate to connect directly to one of the gate pad and the data pad.

This application is a divisional of application Ser. No. 10/815,843,filed Apr. 2, 2004, now U.S. Pat. 7,132,689 now allowed, which claimspriority to Korean Patent Application No. P2003-21116, filed Apr. 3,2003, each of which are incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display having ahorizontal electric field. More particularly, the present inventionrelates to a liquid crystal display and a method of fabricating the samethat are capable of reducing the number of mask processes.

2. Discussion of the Related Art

Generally, liquid crystal displays (LCDs) control light transmittance ofliquid crystal material using an electric field to display a picture.Liquid crystal displays may be classified as a vertical electric fieldtype or a horizontal electric field type based upon a direction of theelectric field that drives the liquid crystal.

The liquid crystal display having a vertical electric field, in which acommon electrode formed on an upper substrate and a pixel electrodeformed on a lower substrate are arranged to face each other, drives aliquid crystal of a twisted nematic mode (TN) by applying a verticalelectric field formed between the common electrode and the pixelelectrode. The liquid crystal display having the vertical electric fieldhas an advantage of a large aperture ratio, but has a narrow viewingangle of about 90°.

The liquid crystal display having a horizontal electric field drives aliquid crystal of an in plane switch (hereinafter referred to as “IPS”)mode by applying a horizontal electric field between the pixel electrodeand the common electrode disposed in parallel on the lower substrate.The liquid crystal display having the applied horizontal electric fieldhas an advantage of an wide viewing angle of about 160°. Hereinafter,the liquid crystal display having the applied horizontal electric fieldwill be described in detail.

The liquid crystal display having the horizontal electric field includesa thin film transistor array substrate (a lower substrate) and a colorfilter array substrate (an upper substrate) that face and are joinedtogether, a spacer to uniformly maintain a cell gap between the upperand lower substrates and a liquid crystal injected into a space providedby the spacer.

The thin film transistor array substrate includes a plurality of signallines for forming a horizontal electric field, a plurality of thin filmtransistors, and an alignment film applied to align the liquid crystalthereon. The color filter array substrate includes a color filter forrepresenting a color, a black matrix for preventing light leakage and analignment film applied for liquid crystal alignment thereon.

In such a liquid crystal display, because the thin film transistor arraysubstrate involves a semiconductor process and requires a plurality ofmask processes, the manufacturing process is complicated and involves ahigh rise factor associated with the manufacturing cost of the liquidcrystal display panel. In order to ease the problems of themanufacturing process, work has been done to develop a thin filmtransistor array substrate having a reduced number of mask processes.This is because one mask process includes many processes such as thinfilm deposition, cleaning, photolithography, etching, photo-resiststripping and inspection processes, etc. Recent development has produceda four-round mask process in which one mask process is reduced from theexistent five-round mask process that is employed as a standard maskprocess.

FIG. 1 is a plan view illustrating a related art thin film transistorsubstrate having a horizontal electric field using the four-round maskprocess, and FIG. 2 is a sectional view of the thin film transistorarray substrate taken along the I-I′ and II-II′ line in FIG. 1.

Referring to FIGS. 1 and 2, the related art thin film transistor arraysubstrate having a horizontal electric field includes a gate line 2 anda data line 4 formed on a lower substrate 45 in such a manner as tocross each other, a thin film transistor 6 formed at each crossing, apixel electrode 14 and a common electrode 18 formed such that thehorizontal electric field is applied in a pixel region defined by thecrossing and a common line 16 connected to the common electrode 18.Further, the related art thin film transistor array substrate includes astorage capacitor 20 formed at an overlapped portion between the pixelelectrode 14 and the common line 16, a gate pad 24 connected to the gateline 2, and a data pad 30 connected to the data line 4 and a common pad36 connected to the common line 16.

The gate line 2 supplies a gate signal to the gate electrode 8 of thethin film transistor 6. The data line 4 supplies a pixel signal to thepixel electrode 14 via a drain electrode 12 of the thin film transistor6. The gate line 2 and the data line 4 cross to define the pixel region5.

The common line 16 is formed in parallel to the gate line 2 in the pixelregion 5 and is positioned to supply a reference voltage for driving theliquid crystal to the common electrode 18.

The thin film transistor 6 responds to the gate signal of the gate line2 so that the pixel signal of the data line 4 is charged to the pixelelectrode 14. To this end, the thin film transistor 6 includes a gateelectrode 8 connected to the gate line 2, a source electrode 10connected to the data line 4 and a drain electrode 12 connected to thepixel electrode 14. Further, the thin film transistor 6 includes anactive layer 48 overlapping the gate electrode 8 with a gate insulatingfilm 46 positioned between the thin film transistor 6 and the gateelectrode 8 and defining a channel between the source electrode 10 andthe drain electrode 12. On the active layer 48, an ohmic contact layer50 for making an ohmic contact with the data line 4, the sourceelectrode 10, the drain electrode 12, the data pad lower electrode 32and the storage electrode 22 is further formed.

The pixel electrode 14, which is connected to the drain electrode 12 ofthe thin film transistor 6 via a first contact hole 13 passing through apassivation film 52, is formed in the pixel region 5. Particularly, thepixel electrode 14 includes a first horizontal part 14A connected to thedrain electrode 12 and formed in parallel with adjacent gate line 2 anda second horizontal part 14B formed to overlap with the common line 16and a finger part 14C formed in parallel with the common electrode 18.

The common electrode 18 is connected to the common line 16 and is formedin the pixel region 5. In addition, the common electrode 18 is formed inparallel with the finger part 14C of the pixel electrode 14 in the pixelregion 5.

A horizontal electric field is applied between the pixel electrode 14,to which the pixel signal is supplied via the thin film transistor 6,and the common electrode 18, to which the reference voltage is suppliedvia the common line 16. Moreover, the horizontal electric field isapplied between the finger part 14C of the pixel electrode 14 and thecommon electrode 18. The liquid crystal molecules arranged in thehorizontal direction between the thin film transistor array substrateand the color filter array substrate by the horizontal electric fieldrotate due to a dielectric anisotropy. The light transmittance of thepixel region 5 differs based upon the amount of rotation of the liquidcrystal molecules and thereby the pictures can be represented.

The storage capacitor 20 consists of the common line 16, a storageelectrode 22 that overlaps with the common line 16 and the gateinsulating film 46, the active layer 48 and the ohmic contact layer 50positioned therebetween, and a pixel electrode 14 connected via a secondcontact hole 21 passing through the storage electrode 22 and thepassivation film 52. The storage capacitor 20 allows a pixel signalcharged in the pixel electrode 14 to be maintained until the next pixelsignal is charged.

The gate line 2 is connected, via the gate pad 24, to a gate driver (notshown). The gate pad 24 consists of a gate pad lower electrode 26extended from the gate line 2, and a gate pad upper electrode 28connected, via a third contact hole 27 passing through the gateinsulating film 46 and the passivation film 52, to the gate pad lowerelectrode 26.

The data line 4 is connected, via the data pad 30, to the data driver(not shown). The data pad 30 consists of a data pad lower electrode 32extended from the data line 4, and a data pad upper electrode 34connected, via a fourth contact hole 33 passing through the passivationfilm 52, to the data pad lower electrode 32.

The common line 16 supplied with the reference voltage from an exteriorreference voltage source (not shown) via the common pad 36. The commonpad 36 consists of a common pad lower electrode 38 extended from thecommon line 16, and a common pad upper electrode 40 connected, via afifth contact hole 39 passing through the gate insulating film 46 andthe passivation film 52, to the common pad lower electrode 38.

A method of fabricating a thin film transistor substrate having theabove-mentioned structure using a four-round mask process will bedescribed in detail with reference to FIGS. 3A to 3D.

In FIG. 3A, a first conductive pattern group including the gate line 2,the gate electrode 8 and the gate pad lower electrode 26 is formed onthe lower substrate 45 using the first mask process.

Specifically, a first metal layer 42 and a second metal layer 44 aresequentially formed on the lower substrate 45 by a deposition techniquesuch as sputtering to form a gate metal layer having a double-structure.Then, the gate metal layer is patterned by a photolithography andetching process using a first mask to form the first conductive patterngroup including the gate line 2, the gate electrode 8, the gate padlower electrode 26, the common line 16, common electrode 18 and thecommon pad lower electrode 38. The first metal layer 42 is formed withan aluminum system metal and the second metal layer 44 is formed with achrome (Cr) or a molybdenum (Mo).

Referring to FIG. 3B, the gate insulating film 46 is formed on the lowersubstrate 45 provided with the first conductive pattern group. Further,a semiconductor pattern group including the active layer 48 and theohmic contact layer 50 and a second conductive pattern group includingthe data line 4, the source electrode 10, the drain electrode 12, thedata pad lower electrode 32 and the storage electrode 22 are formed onthe gate insulating film 46 using the second mask process.

More specifically, the gate insulating film 46, a first semiconductorlayer, a second semiconductor layer and a data metal layer aresequentially formed on the lower substrate 45 provided with the firstconductive pattern group by deposition techniques such as the plasmaenhanced chemical vapor deposition (PECVD) and the sputtering, etc. Thegate insulating film 46 is made of an inorganic insulating material suchas silicon oxide (SiOx) or silicon nitride (SiNx). The firstsemiconductor layer is made of amorphous silicon in which an impurity isnot doped and the second conductor layer is made of amorphous siliconthat an impurity of a N type or P type is doped. The data metal layer ismade of a molybdenum (Mo), a titanium (Ti), tantalum (Ta) or amolybdenum alloy, etc.

Then, a photo-resist pattern is formed on the data metal layer byphotolithography using a second mask. In this case, a diffractiveexposure mask having a diffractive exposing part at a channel portion ofthe thin film transistor is used as a second mask, allowing aphoto-resist pattern of the channel portion to have a lower height thanother photo-resist patterns of region portions.

Subsequently, the data metal layer is patterned by a wet etching processusing the other photo-resist patterns to provide the data patternincluding the data line 4, the source electrode 10, the drain electrode12 being integral to the source electrode 10 and the storage electrode22.

Next, the first semiconductor layer and the second semiconductor layerare patterned at the same time by a dry etching process using the samephoto-resist pattern to provide the ohmic contact layer 50 and theactive layer 48.

The photo-resist pattern having a relatively low height is removed fromthe channel portion by an ashing process and thereafter the sourceelectrode, the drain electrode and the ohmic contact layer 50 of thechannel portion are etched by the dry etching process. Thus, the activelayer 48 of the channel portion is exposed to separate the sourceelectrode 10 from the drain electrode 12.

Then, a remainder of the photo-resist pattern on the second conductivepattern group is removed using the stripping process.

Referring to FIG. 3C, the passivation film 52 including first to fifthcontact holes 13, 21, 27, 33 and 39 are formed on the gate insulatingfilm 46 provided with the second conductive pattern group using a thirdmask process.

More specifically, the passivation film 52 is entirely formed on thegate insulating film 46 provided with the data pattern by a depositiontechnique such as plasma enhanced chemical vapor deposition (PECVD). Thepassivation film 52 is patterned by the photolithography and the etchingprocess using the third mask to form first to fifth contact holes 13,21, 27, 33 and 39. The first contact hole 13 is formed in such a mannerto pass through the passivation film 52 and expose the drain electrode12, whereas the second contact hole 21 is formed in such a manner as topass through the passivation film 52 and expose the storage electrode22. The third contact hole 27 is formed in such a manner as to passthrough the passivation film 52 and the gate insulating film 46 andexpose the gate pad lower electrode 26, whereas the fourth contact hole33 is formed in such a manner as to pass through the passsivation film52 and expose the data pad lower electrode 32, and the fifth contacthole 39 is formed in such a manner as to pass through the passivationfilm 52 and the gate insulating film 46 and expose the common pad lowerelectrode 38. Herein, when a metal, which has a high ratio of dryetching like a molybdenum (Mo), is used for the data metal, the firstcontact hole 13, the second contact hole 21 and the forth contact hole33 are formed in such a manner to pass through to the drain electrode12, the storage electrode 22 and the data pad lower electrode 32,respectively, to expose their side.

The passivation film 52 is made of an inorganic insulating material suchas the gate insulating film 46 or an organic insulating material havinga small dielectric constant such as an acrylic organic compound, BCB(benzocyclobutene) or PFCB (perfluorocyclobutane), etc.

In FIG. 3D, a third conductive pattern group including the pixelelectrode 14, the gate pad upper electrode 28, the data pad upperelectrode 34 and the common pad upper electrode 40 is formed on thepassivation film 52 using the fourth mask process.

More specifically, a transparent conductive film is coated on thepassivation film 52 using a deposition technique such as the sputtering,etc. Then, the transparent conductive film is patterned by thephotolithography and the etching process using a fourth mask, to providethe third conductive pattern group including the pixel electrode 14, thegate pad upper electrode 28, the data pad upper electrode 34 and thecommon pad upper electrode 40. The pixel electrode 14 is electricallyconnected, via the first contact hole 13, to the drain electrode 12while being electrically connected, via the second contact hole 21, tothe storage electrode 22. The gate pad upper electrode 28 iselectrically connected, via the third contact hole 37, to the gate padlower electrode 26. The data pad upper electrode 34 is electricallyconnected, via the fourth contact hole 33, to the data pad lowerelectrode 32. The common pad upper electrode 40 is electricallyconnected, via the fifth contact hole 39, to the common pad lowerelectrode 38.

In this connection, the transparent conductive film may be made of anindium-tin-oxide (ITO), a tin-oxide (TO), an indium-zinc-oxide (IZO) oran indium tin zinc oxide (ITZO).

As described above, the related art thin film transistor array substratehaving a horizontal electric field and the manufacturing method thereofuses a four-round mask process. Thus, the number of manufacturingprocesses is reduced in comparison to a five-round mask process, andhence manufacturing costs are also reduced. However, because thefour-round mask process still has a complex manufacturing process, thereis a need to further simplify the manufacturing process and reduce themanufacturing costs more.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay having an applied horizontal electric field and a method offabricating the same that substantially obviates one as more of theproblems due to limitations and disadvantages of the related art

An advantage of the present invention is to provide a liquid crystaldisplay device and method that reduces the number of mask processes.

To achieve this and other advantages and in accordance with theinvention as embodied and broadly described, the liquid crystal displayhaving an applied horizontal electric field includes: a gate line; acommon line substantially parallel to the gate line; a data linearranged to cross the gate line and the common line to define a pixelarea; a thin film transistor formed at each crossing of the gate lineand the data line; a common electrode formed in the pixel area andconnected to the common line; a pixel electrode connected to the thinfilm transistor, wherein the horizontal electric field is formed betweenthe pixel electrode and the common electrode in the pixel area; a gatepad formed with at least one conductive layer included in the gate line;a data pad formed with at least one conductive layer included in thedata line; a common pad formed with at least one conductive layerincluded in the common line; a passivation film to expose at least oneof the gate pad, the data pad and the common pad; and a drivingintegrated circuit mounted on a substrate directly connected to one ofthe gate pad and the data pad.

In another aspect of the present invention, a method for fabricating aliquid crystal display having a horizontal electric field includes:preparing a thin film transistor array substrate having a gate line anda data line, wherein a thin film transistor formed at a crossing of thegate line and the data line, wherein the horizontal electric field isformed between a pixel electrode connected to the thin film transistorand a common electrode forming a conductive layer in a gate pad, a datapad, and a common pad, wherein at least one of the gate pad, data padand common pad is exposed through a passivation layer, and mounting adriving integrated circuit on the substrate, wherein at least one of theexposed gate pad and the data pad is directly connected to the drivingintegrated circuit.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the invention will be apparent from thefollowing detailed description of the embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 is a plan view showing a related art thin film transistor arraysubstrate of a liquid crystal display having an applied horizontalelectric field;

FIG. 2 is a sectional view of the thin film transistor array substratetaken along the lines I-I′ and II-II′ in FIG. 1;

FIGS. 3A to 3D are sectional views sequentially illustrating a method ofmanufacturing the thin film transistor array substrate shown in FIG. 2;

FIG. 4 is a plan view showing a thin film transistor array substrate ofthe liquid crystal display having an applied horizontal electric fieldaccording to an embodiment of the present invention;

FIG. 5 is a sectional view of the thin film transistor array substratetaken along the lines III-III′ and IV-IV′ in FIG. 4;

FIG. 6A and FIG. 6B are a plan view and a sectional view for explaininga first mask process among a manufacturing method of a thin filmtransistor array substrate according to an embodiment of the presentinvention, respectively;

FIGS. 7A to 7C are sectional views for illustrating the first maskprocess of the manufacturing method of a thin film transistor arraysubstrate according to an embodiment of the present invention;

FIGS. 8A and 8B are a plan view and a sectional view, respectively, forexplaining a second mask process of the manufacturing method of the thinfilm transistor array substrate according to an embodiment of thepresent invention;

FIGS. 9A to 9E are sectional views for illustrating the second maskprocess of the manufacturing method of the thin film transistor arraysubstrate according to an embodiment of the present invention;

FIGS. 10A and 10B are a plan view and a sectional view, respectively,illustrating a third mask process among the manufacturing method of thethin film transistor array substrate according to an embodiment of thepresent invention;

FIGS. 11A to 11C are sectional views illustrating the third mask processof the manufacturing method of the thin film transistor array substrateaccording to an embodiment of the present invention;

FIG. 12 is a sectional view showing pads of a first structure of thethin film transistor substrate according to an embodiment of the presentinvention;

FIG. 13 is a sectional view showing pads of a second structure of thethin film transistor substrate according to an embodiment of the presentinvention;

FIG. 14 is a plan view showing a liquid crystal display having the thinfilm transistor array substrate shown in FIG. 4;

FIG. 15 is a sectional view of the liquid crystal display shown in FIG.14;

FIG. 16 is a plan view illustrating another liquid crystal displayhaving the thin film transistor array substrate shown in FIG. 4; and

FIG. 17 is a sectional view of the liquid crystal display shown in FIG.16.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an embodiment of the presentinvention, example of which is illustrated in the accompanying drawings.

FIG. 4 is a plan view illustrating a thin film transistor arraysubstrate of a liquid crystal display having an applied horizontalelectric field according to an embodiment of the present invention, andFIG. 5 is a sectional view of the thin film transistor array substratetaken along the lines III-III′ and IV-IV′ of FIG. 4.

In FIGS. 4 and 5, the thin film transistor array substrate includes agate line 102 and a data line 104, which have a gate insulating film 146therebetween, formed on a lower substrate 145 in such a manner as tocross each other, a thin film transistor 106 formed at each crossing ofthe gate line 102 and the data line 104, a pixel electrode 114 and acommon electrode 118 formed in order to apply the horizontal electricfield in a pixel region defined by the interconnection and a common line116 connected to the common electrode 118. Further, the thin filmtransistor array substrate includes a storage capacitor 120 formed at anoverlapped portion between an upper storage electrode 122 and the commonline 116, a gate pad 124 extended from the gate line 102, and a data pad130 extended from the data line 104 and a common pad 136 extended fromthe common line 116.

The gate line 102 for supplying a gate signal and the data line 104 forsupplying a data signal are formed in a crossing structure to therebydefine a pixel region 105.

The common line 116 supplies a reference voltage for driving the liquidcrystal and is formed in parallel to the gate line 102 within the pixelregion 105.

The thin film transistor 106 responds to the gate signal of the gateline 102 so that the pixel signal of the data line 104 is charged andmaintained in the pixel electrode 114. To this end, the thin filmtransistor 106 includes a gate electrode 108 connected to the gate line102, a source electrode included in the data line 104 and a drainelectrode 112 connected to the pixel electrode 114. Further, the thinfilm transistor 106 includes an active layer 148 overlapping with thegate electrode 108 with a gate insulating film 146 positionedtherebetween and defining a channel between the source electrode and thedrain electrode 112.

The active layer 148 is formed to overlap with the data line 104, thedata pad 130 and an upper storage electrode 122. On the active layer148, an ohmic contact layer 150 for making an ohmic contact with thedata line 104, the drain electrode 112, the data pad 130 and the upperstorage electrode 122 is further provided.

The pixel electrode 114 being integral to the drain electrode 112 of thethin film transistor 106 and the upper storage electrode 122 is formedin the pixel region 105. Particularly, the pixel electrode 114 includesa horizontal part 114A extended in parallel with adjacent gate line 102from the drain electrode 112 and a finger part 114B extended from thehorizontal part 114A in vertical direction.

The common electrode 118 is connected to the common line 116 and isformed in the pixel region 105. Specially, the common electrode 118 isformed in parallel with the finger part 114B of the pixel electrode 114in the pixel region 105.

Accordingly, a horizontal electric field is formed between the pixelelectrode 114, to which the pixel signal is supplied via the thin filmtransistor 106, and the common electrode 118, to which the referencevoltage is supplied via the common line 116. Specifically, thehorizontal electric field is applied between the finger part 114B of thepixel electrode 114 and the common electrode 118. The liquid crystalmolecules arranged in the horizontal direction between the thin filmtransistor array substrate and the color filter array substrate by thehorizontal electric field rotate due to a dielectric anisotropy.Further, the light transmittance of the pixel region 105 differs inaccordance with a rotation amount of the liquid crystal molecules andpictures can be represented.

The storage capacitor 120 consists of the common line 116 and the upperstorage electrode 122 overlapping with the common line 116 with the gateinsulating film 146, the active layer 148 and the ohmic contact layer150 therebetween and being integral with the pixel electrode 114. Thestorage capacitor 120 allows a pixel signal charged in the pixelelectrode 114 to be maintained until the next pixel signal is charged.

The gate line 102 is connected, via the gate pad 124, to a gate driverintegrated circuit (IC)(not shown) mounted on a tape carried package(TCP). The gate pad 124 is extended from the gate line 102 and isexposed through a first contact hole 127 passing through a gateinsulating film 146 and a passivation film 152. The gate pad 124 has anexposed structure of a metal layer that has a relatively high strengthand corrosion resistance such as a titanium (Ti) and a tungsten (W)included in the gate line 102.

The common line 116 may be supplied with the reference voltage from anexterior power source (not shown) via the common pad 136. The common pad136 is extended from the common line 116 and is exposed through a thirdcontact hole 127 passing through a gate insulating film 146 and apassivation film 152. The common pad 136 has an exposed structure ofmetal layer such as a titanium (Ti) and a tungsten (W) as similar as thegate pad 124.

The gate line 102, the gate electrode 108, the common line 116 andcommon electrode 118 may have a double-layer structure of metal layerswith a first and a second metal layer 142 and 144. Among the metallayers, a metal layer may be made of a metal that has a relatively highstrength and corrosion resistance such as a titanium (Ti) and a tungsten(W). while the other metal layer may be made of a low resistance metalsuch as an aluminum (Al) system metal, a molybdenum (Mo) and a copper(Cu) that are conventionally employed as a gate metal.

In a case in which the first metal layer 142 is made of a metal that hasa high strength and corrosion resistance, the gate pad 124 and thecommon pad 136 have an exposed structure in which the second metal layer144 of an upper portion is removed and the first metal layer 142 of thelower portion is exposed. On the other hand, in a case in which thesecond metal layer 144 is made of a metal that has a high strength andcorrosion resistance, the gate pad 124 and the common pad 136 have anexposed structure in which the second metal layer 144 of an upperportion is exposed.

The data line 104 is connected to a data driver IC (not shown) mountedon a TCP via the data pad 130. The data pad 130 is extended from thedata line 104 and is exposed through a second contact hole 133 passingthrough a passivation film 152. The data pad 130 has an exposedstructure of the metal layer that has a relatively high strength andcorrosion resistance such as titanium (Ti) and tungsten (W) included inthe data line 104. The data pad 130 of metal layer is connected to theTCP in which the data drive IC mounted thereon via antistrophicconductive film (ACF) having a conductive ball. Accordingly, althoughthe process of attaching the data pad 130 and the TCP is repeatedlyperformed, the defect caused by the opening of the data pad 130 does notoccur.

More specifically, the data line 104, the drain electrode 112, the pixelelectrode 114 and the upper storage electrode 122 have a double-layerstructure of metal layers stacked with a first and a second metal layers154 and 156. One metal layer of the metal layers is made of a metal thathas a relatively high strength and corrosion resistance such as atitanium (Ti) and a tungsten (W). Whereas, the second metal layer ismade of a low resistance metal such as an aluminum (Al) system metal, amolybdenum (Mo) and a copper (Cu) that are generally employed as a gatemetal.

In a case in which the first metal layer 154 is made of a metal having ahigh strength and corrosion resistance, the data pad 130 has an exposedstructure in which the second metal layer 156 of an upper portion isremoved and the first metal layer 154 of a lower portion is exposed. Onthe other hand, in a case in which the second metal layer 156 is made ofa metal having a high strength and corrosion resistance, the data pad130 has an exposed structure in which the second metal layer 156 of anupper portion is exposed.

FIGS. 6A and 6B are a plan view and a sectional view, respectively, forexplaining a first mask process of a manufacturing method of the thinfilm transistor array substrate having a horizontal electric field shownin FIGS. 4 and 5, respectively.

As shown in FIGS. 6A and 6B, a first conductive pattern group includingthe gate line 102, the gate electrode 108 and the gate pad 124, thecommon line 116, the common electrode 118 and the common pad 136 isformed on the lower substrate 145 using the first mask process.

The first mask process is explained with reference to FIGS. 7A to 7C.

A first gate metal layer 142 and a second gate metal layer 144 aresequentially formed on the lower upper substrate 145 by a depositionmethod such as sputtering, to form a gate metal layer having adouble-layer structure as shown in FIG. 7A. Either one of the first gatemetal layer 142 and the second gate metal layer 144 may be made of anymetal that has a relatively high strength and corrosion resistance suchas a titanium (Ti) and a tungsten (W), while another metal layer may bemade of a metal such as an aluminum (Al) system metal, a molybdenum (Mo)and a copper (Cu). After the gate metal layer is formed, a photo-resistfiled is formed entirely on the second gate metal layer 144 and then afirst mask 300 is arranged on the lower substrate 145 as shown in FIG.7B. The first mask 300 includes a mask substrate 304 which is atransparent material and a cut-off part formed on a cut-off region P2 ofthe mask substrate 304. A exposed region in which the mask substrate 304is exposed becomes an exposure region P1. The photo-resist film isexposed and developed using the first mask 300 as set forth above, toform the photo-resist pattern 306 in the cut-off region P2 correspondingto the cut-off part 302 of the first mask 300. In FIG. 7C, the first andthe second gate metal layer 142 and 144 are patterned by an etchingprocess using the photo-resist pattern 306, to form the first conductivepattern group including the gate line, the gate electrode 108, the gatepad 124, the common line 116, the common electrode 118 and the commonpad 136.

FIGS. 8A and 8B are a plan view and a sectional view for explaining asecond mask process for the manufacturing method of the thin filmtransistor array substrate having an applied horizontal electric fieldaccording to an embodiment of the present invention.

A gate insulating film 146 is formed on the lower substrate 145 providedwith the first conductive pattern group by a deposition method such asthe plasma enhanced chemical vapor deposition (PECVD) or sputtering. Thegate insulating film 146 is made of an inorganic insulating materialsuch as silicon oxide (SiOx) or silicon nitride (SiNx).

Further, as shown in FIGS. 8A and 8B, a semiconductor pattern groupincluding an active layer 148 and the ohmic contact layer 150 and asecond conductive pattern group including the data line 104, the drainelectrode 112, the pixel electrode 114, the data pad 130 and the upperstorage electrode 122 are formed on the gate insulating film 146 usingthe second mask process. The second mask process is explained withreference to FIGS. 9A to 9E.

As shown in FIG. 9A, on the gate insulating film 146, a firstsemiconductor layer 147, a second semiconductor layer 149, a first and asecond source/drain metal layer 154 and 156 are sequentially provided bydeposition techniques such as plasma enhanced chemical vapor deposition(PECVD) and sputtering, etc. The first semiconductor layer 147 may bemade of amorphous silicon in which an impurity is not doped, and thesecond conductor layer 149 may be made of amorphous silicon in which animpurity of a N type or P type is doped. Any one of the first and thesecond source/drain metal layers 154 and 156 may be made of a metal thathas a relatively high strength and corrosion resistance such as atitanium (Ti) and a tungsten (W), while the other metal layer may bemade of a metal such as an aluminum (Al) system metal, a molybdenum (Mo)and a copper (Cu).

Next, a photo-resist film is formed on the second source/drain metallayer 156 and then a second mask 160 used for a partial exposure isarranged on the lower substrate 145 as shown in FIG. 9B. The second mask160 includes a mask substrate 162 which is a transparent material, acut-off part 164 formed on a cut-off region P2 of the mask substrate 162and a diffractive exposure part 166 (or a semi-transmitting part) formedon a partial exposure region P3 of the mask substrate 162. A region inwhich the mask substrate 162 is exposed is an exposure region P1. Thephoto-resist film is exposed and then developed using the second mask160 as set forth above, to form the photo-resist pattern 168 which has astepped part in the cut-off region P2 and the partial exposure region P3corresponding to the diffractive exposure part 166 and cut-off part 164of the second mask 160. More particularly, the photo-resist pattern 168formed in the partial exposure region P3 has a second height H2 that islower than a first height H1 of the photo-resist pattern 168 formed inthe cut-off region P2.

Subsequently, the first and the second source/drain metal layer 154 and156 are patterned by a wet etching process using the photo-resistpattern 168, so that the second conductive pattern group including thedata line 104, the drain electrode 112 being integral to the sourceelectrode connected to the data line 104, the pixel electrode 114, theupper storage electrode 122 and the data pad 130 is formed as shown inFIG. 9C.

In FIG. 9D, the first semiconductor layer 147 and the secondsemiconductor layer 149 are patterned by a dry etching process using thephoto-resist pattern 168 as a mask to provide the ohmic contact layer150 and the active layer 148 along the second conductive pattern group.Next, the photo-resist pattern 168 formed with the second height H2 inthe partial exposure region P3 is removed by the ashing process using anoxygen (O2) plasma, while the photo-resist pattern 168 formed with thefirst height H1 in the cut-off region P2 has a lowered height. Thepartial exposure region P3 by the etching process using the photo-resistpattern 168, that is, the first and the second source/drain metal layers154 and 156 formed at a channel portion of the thin film transistor areremoved. In a case in which the second source/drain metal layer 156 ismade of molybdenum Mo and the first source/drain metal layer 154 is madeof titanium Ti, the second source/drain metal layer 156 is removed inthe channel portion by a dry etching process and the first source/drainmetal layer 154 is removed by a wet etching process in the channelportion. In a case in which the second source/drain metal layer 156 ismade of titanium Ti and the first source/drain metal layer 154 is madeof molybdenum Mo, the second source/drain metal layer 156 is removed bya wet etching process in the channel portion and the first source/drainmetal layer 154 is removed by a dry etching process in the channelportion. Accordingly, the drain electrode 112 is separated from the dataline 104 including the source electrode. Thereafter, the ohmic contactlayer 150 is removed by a dry etching process using the photo-resistpattern 168 to expose the active layer 148.

In FIG. 9E, the photo-resist pattern 168 left on the second conductivepattern group is removed by a stripping process.

FIGS. 10A and 10B are a plan view and a sectional view, respectively,for explaining a third mask process of the manufacturing method of thethin film transistor array substrate according to an embodiment of thepresent invention, respectively.

The passivation film 152 including first to third contact holes 127, 133and 139 is formed on the gate insulating film 146 stacked with thesemiconductor pattern and a second conductive pattern group by the thirdmask process as shown in FIGS. 10A and 10B. The third mask process isexplained with reference to FIGS. 11A to 11C.

The passivation film 152 may be formed by a deposition technique such asplasma enhanced chemical vapor deposition (PECVD) on the gate insulatingfilm 146 where the semiconductor pattern and the source/drain metalpattern are stacked. The passivation film 152 may be made of aninorganic material such as the gate insulating film 146 or an organicmaterial having a small dielectric constant such as an acrylic organiccompound, BCB (benzocyclobutene) or PFCB (perfluorocyclobutane), etc.Subsequently, in FIG. 11B, the photo-resist film is formed entirely onthe passivation film 152 and the third mask 310 is arranged on the lowersubstrate 145 as shown in FIG. 11B. The third mask 310 includes a masksubstrate 314 which is a transparent material, a cut-off part 312 formedin a cut-off region P2 of the mask substrate 314. A region in which themask substrate 314 is exposed is an exposure region P1. The photo-resistfilm is exposed and then developed using the third mask 310 to form thephoto-resist pattern 316 in the cut-off region P2 based upon the cut-offpart 312 of the third mask 310. The passivation film 152 is patterned bythe etching process using the photo-resist pattern 316 to thereby formthe first to the third contact holes 127, 133 and 139.

In FIG. 11C, the first contact hole 127 is formed in such a manner topass through the passivation film 152 and the gate insulating film 146and expose the gate pad 124, the second contact hole 133 is formed insuch a manner to pass through the passivation film 152 and expose thedata pad 130, and the third contact hole 139 is formed in such a mannerto pass through the passivation film 152 and the gate insulating film146 and expose the common pad 136. The exposed gate pad 124, the datapad 130 and the common pad 136 have an exposed structure of metal thathas a high strength and corrosion resistance. In this case, the gate pad124, the data pad 130 and the common pad 136 have two structures asshown in FIGS. 12 and 13.

For example, in a case in which the first gate metal layer 142 of alower portion is made of a titanium Ti and the second gate metal layer144 of an upper portion is made of a molybdenum Mo, the gate pad 124 andthe common pad 136 consists of only the first gate metal layer 142 ofthe lower portion as shown in FIG. 12. This is because the second gatemetal layer 144 of the upper portion is removed by the etching processemployed to form the first and the third contact hole 127 and 139.

On the contrary, in a case in which the first gate metal layer 142 ofthe lower portion is made of a molybdenum Mo and the second gate metallayer 144 of the upper portion is made of a titanium Ti, the gate pad124 and the common pad 136 have a double-layer structure of metal layersin which the first and the second gate metal layers 142 and 144 arestacked as shown in FIG. 13. Also, the gate pad 124 and the common pad136 have an exposed structure of the gate metal layer 144 of the upperportion through the use of the first and the third contact hole 127 and139.

Further, in case where the first source/drain metal layer 154 of thelower portion is made of a titanium Ti and the second source/drain metallayer 156 of the upper portion is made of a molybdenum Mo, the data pad130 is consisted of only the first source/drain metal layer 154 of thelower portion as shown in FIG. 12. This is because the secondsource/drain metal layer 156 is removed for the etching process employedto form the second contact hole 133.

On the contrary, in case where the first source/drain metal layer 154 ofthe lower portion is made of a molybdenum Mo and the second source/drainmetal layer 156 is made of a titanium Ti, the data pad 130 has adouble-layer structure of metal layers in which the first and the secondsource/drain metal layers 154 and 156 are stacked as shown in FIG. 13.Also, the data pad 130 has an exposed structure of the source/drainmetal layer 156 of the upper portion through the use of the secondcontact hole 133.

As described above, in an embodiment of thin film transistor arraysubstrate having a horizontal electric field and the method offabricating thereof of the present invention, the pixel electrode 114 isformed of a metal similar to the drain electrode 112. Further, the gatepad 124, the data pad 130 and the common pad 136 use a metal that has ahigh strength and corrosion resistance enough to prevent the defectcaused by the opening of the pad irrespective of the repeated process ofattaching the TCP. Accordingly, a transparent conductive film is free inthe present invention, that is, the process including the transparentconductive film deposition process and patterning process isunnecessary, which permits the reduction of one mask process. In otherwords, the thin film transistor array substrate having an appliedhorizontal electric field according to the present invention is formedusing a three-round mask process.

The thin film transistor array substrate formed using the three-roundmask process and the color filter array substrate formed using aseparate process are prepared and combined and then a liquid crystal isinjected therebetween, to fabricate a liquid panel. In this case, thecolor filter array substrate is combined with the thin film transistorarray substrate to expose a pad region where the gate pad 124, the datapad 130 and the common pad 136 are formed on the thin film transistorarray substrate.

FIG. 14 is a plan view representing a liquid crystal display accordingto the present invention, and FIG. 15 is a sectional view representingthe liquid crystal display shown in FIG. 14.

Referring to FIGS. 14 and 15, the liquid crystal display according tothe present invention includes a gate drive IC 264 mounted on a lowersubstrate 145 of a liquid crystal panel 208 and a data drive IC 272mounted on a TCP 180.

The gate drive ICs 264 are mounted by a COG (a Chip on Glass) system onthe lower substrate 145 and are connected to gate lines 102 via the gatepad 124 to supply a gate signal to the gate lines 102.

Gate control signals and power source signals from a timing controllerand a power source portion (not shown) on a PCB (a Printed CircuitBoard) 270 are supplied to a signal supplying line 274 via the data TCP180. The signal supplying line 274 is connected to an input terminal ofthe gate drive ICs 264 through an input bump and supplies the gatecontrol signals and the power source signals to the gate drive IC 264.The gate drive IC 264 makes a gate-driving signal using the gate controlsignals and the power source signals. The gate driving signals aresupplied to the gate pad 124 through an output bump 260 connected tooutput terminals 262 of the gate drive IC 264.

The data drive ICs 272 are mounted by a TAB (a Tape Automated Bonding)system on the TCP 180 and are connected to data lines 104 via a data pad130. Specifically, the TCP 180, which the data drive ICs 272 aremounted, is attached using an ACF (an Antistrophic Conductive Film) 182including a conductive ball 184 on a data pad region. Accordingly,output pads 176 formed on a base film 172 of the TCP 180 areelectrically connected to the data pad 130, via the ACF 182. Further anyone of dummy output pads 178 formed on the base film 172 of the TCP 180on which the data drive ICs 272 are mounted is electrically connected tothe common pad 136 via the ACF 182.

FIG. 16 is a plan view representing another type of liquid crystaldisplay according to the present invention and FIG. 17 is a sectionalview representing the liquid crystal display shown in FIG. 16.

Referring to FIGS. 16 and 17, the liquid crystal display according tothe present invention includes a gate drive IC 264 and a data drive ICmounted on a lower substrate 145 of a liquid crystal panel 208 and a FPC(a Flexible Printed Circuit) 280 for supplying a driving signal to the264 and 267.

The data drive ICs 272 are mounted by a COG (a Chip on Glass) system onthe lower substrate 145 and is connected to data lines 104 via the datapad 130.

As an example, data control signals and data signals from a timingcontroller and a power source portion not shown on a PCB 270 aresupplied to a signal supplying line 274 via the FPC 280 and a COGconnector 288. The signal supplying line 274 is connected to an inputterminal of the data drive ICs 272 through an input bump and suppliesthe data control signals and the data signals to the data drive IC 272.The data drive IC 272 makes a data-driving signal using the data controlsignals and the data signals. The data driving signals are supplied tothe data pad 130 through an output bump 286 connected to outputterminals 284 of the data drive IC 272.

The gate drive ICs 264 are mounted by COG system on the lower substrate145 and are connected to gate lines 102 via the gate pad 124.

Gate control signals and power source signals from a timing controllerand a power source portion not shown on PCB 270 are supplied to a signalsupplying line 274 via the FPC 280 and the COG connector 288. The signalsupplying line 274 is connected to an input terminal of the gate driveICs 264 through an input bump and supplies the gate control signals andthe power source signals to the gate drive IC 264. The gate drive IC 264makes a gate-driving signal using the gate control signals and the powersource signals. The gate driving signals are supplied to the gate pad124 through an output bump 260 connected to output terminals 262 of thegate drive IC 264.

The FPC 280 supplies gate control signals and power source signals fromthe timing controller and a power source portion to its correspondingdrive ICs 264 and 272. That is, input pad of the FPC is connected to thePCB 279 and output pad of the FPC 280 is connected to the COG connector288 of the signal supplying line 274.

Further, any one of output pad 282 of the FPC 280 is connected to thecommon pad 136 using the ACF 182 including the conductive ball 184 andsupplies reference voltage for driving liquid crystal to the common line116.

Any one of the gate drive IC 264 and the data drive IC 272 may bemounted by the COG system on the lower substrate such that corrosion ofexposed metal layer in the exposed gate pad 124, the exposed data pad130 and the common pad 136 is prevented.

In the thin film transistor array substrate having a horizontal electricfield and the manufacturing method thereof, the pixel electrode isformed of metal identical to the drain electrode, and the pads have thestructure wherein a metal layer having a high strength and corrosionresistance is exposed in order to prevent the defect caused by theopening. Accordingly, it is possible to manufacture the thin filmtransistor array substrate using the three-round mask process andsimplify the structure and processes of the thin film transistor arraysubstrate, and reduce the manufacturing cost and improve the manufactureyield.

Further, the liquid crystal display having a horizontal electric fieldand the manufacturing method thereof according to a second embodiment ofthe present invention are capable of preventing corrosion of a metallayer of an exposed pad due to a drive IC mounted by a COG systemdirectly on a substrate.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for fabricating a liquid crystal display having a horizontalelectric field comprising: preparing a thin film transistor arraysubstrate having a gate line and a data line, wherein a thin filmtransistor is formed at a crossing of the gate line and the data line,wherein the horizontal electric field is formed between a pixelelectrode connected to the thin film transistor and a common electrode;forming a conductive layer in a gate pad, a data pad, and a common pad,wherein an entire upper surface of the gate pad, data pad and common padis surrounded and exposed through a passivation film; and mounting adriving integrated circuit on the substrate, wherein at least one of theexposed gate pad and the data pad is directly connected to the drivingintegrated circuit.
 2. The method according to claim 1, wherein mountingthe driving integrated circuit on the substrate includes directlyconnecting the gate pad to the driving integrated circuit.
 3. The methodaccording to claim 2, further including directly connecting the data padto the driving integrated circuit.
 4. The method according to claim 2,wherein mounting the driving integrated circuit on the substrate furtherincludes connecting the data pad with the driving integrated circuitusing a conductive film.
 5. The method according to claim 1, whereinpreparing the thin film transistor substrate includes: forming, on thesubstrate, a first conductive pattern group including the gate line, agate electrode connected to the gate line, a common line, the commonelectrode, the gate pad and the common pad wherein the common line issubstantially in parallel to the gate line; forming a gate insulatingfilm on the substrate having the first conductive pattern group thereon;forming a semiconductor layer at a predetermined area of the gateinsulating film and a second conductive pattern group having the dataline, the data pad a source electrode of the thin film transistorconnected with the data line, a drain electrode of the thin filmtransistor being opposite to the source electrode, a pixel electrodeconnected to the drain electrode and substantially parallel to thecommon electrode and the data line; and forming a passivation film toexpose the gate pad, the data pad and the common pad on the gateinsulation film having the second conductive pattern group and thesemiconductor layer formed thereon.
 6. The method according to claim 5,wherein the first conductive pattern group is formed to have adouble-layer structure including a main conductive layer and a secondaryconductive layer formed of a metal that has a relatively high strengthand corrosion resistance, and wherein the secondary conductive layer ofthe gate pad and common pad protects against an opening of the mainconductive layer of the gate pad and the common pad.
 7. The methodaccording to claim 6, wherein forming the passivation film includesexposing the secondary conductive layer of the gate pad and the commonpad.
 8. The method according to claim 6, wherein forming the passivationfilm includes forming a contact hole that passes through the passivationfilm and the gate insulating film to expose the secondary conductivelayer.
 9. The method according to claim 6, wherein the forming thepassivation film includes forming a contact hole that passes through thepassivation film, the gate insulation film and the main conductive layerto expose the secondary conductive layer.
 10. The method according toclaim 6, wherein the main layer includes at least one of an aluminumsystem metal, a copper, a molybdenum, a chrome and a tungsten which is alow resistance metal, and wherein the secondary conductive layerincludes a titanium.
 11. The method according to claim 5, wherein thesecond conductive pattern group having the data line, the data pad, thesource electrode, the drain electrode, and the pixel electrode is formedto have a double-layer structure including a main conductive layer and asecondary conductive layer formed of a metal that has a relatively highstrength and corrosion resistance, and wherein the secondary conductivelayer of the data pad protects against an opening of the main conductivelayer of the data pad.
 12. The method according to claim 11, whereinforming the passivation film includes exposing the secondary conductivelayer of the data pad.
 13. The method according to claim 11, whereinforming the passivation film includes forming a contact hole that passesthrough the passivation film to expose the secondary conductive layer.14. The method according to claim 11, wherein forming the passivationfilm includes forming a contact hole that passes through the passivationfilm and the main conductive layer of the data pad to expose thesecondary conductive layer.
 15. The method according to claim 11,wherein the main conductive layer includes at least one of an aluminumsystem metal, a copper, a molybdenum, a chrome and a tungsten which is alow resistance metal, and wherein the secondary conductive layerincludes a titanium.